Technical Field
This disclosure relates generally to computer-assisted techniques for creating dental restorations.
Brief Description of the Related Art
The art of fabricating custom-fit prosthetics in the dental field is well-known. Prosthetics are replacements for tooth or bone structure. They include restorations, replacements, inlays, onlays, veneers, full and partial crowns, bridges, implants, posts, and the like. Typically, a dentist prepares a tooth for a restoration by removing existing anatomy, which is then lost. The resultant prepared area (a “preparation”) is then digitized (or, in the alternative, a dental impression is taken) for the purpose of constructing a restoration, appliance or substructure. The restoration itself may be constructed through a variety of techniques including manually constructing the restoration, using automated techniques based on computer algorithms, or a combination of manual and automated techniques.
Computer-assisted techniques have been developed to generate three-dimensional (“3D”) visual images of physical objects, such as a dental preparation. In general, the 3D image may be generated by a computer that processes data representing the surfaces and contours of a physical object. The computer displays the 3D image on a screen or a computer monitor. The computer typically includes a graphical user interface (GUI). Data is generated by optically scanning the physical object and detecting or capturing the light reflected off of the object. Based on processing techniques, the shape, surfaces and/or contours of the object may be modeled by the computer. During the process of creating a tooth restoration model, one or more user interface tools may be provided to facilitate the design process. One known display technique uses a computer monitor that, under software control, displays a 3-dimensional representation of a tooth model.
It is also known in the art to use such computer-aided design systems to facilitate the production of a crown to be placed on a custom implant abutment. Because the implant abutment is custom designed (i.e., to fit the implant), the interior of the crown that attaches to the abutment also needs to be custom designed for the particular case. The usual process followed is for an implant to be inserted into the jawbone (or maxillary-upper arch) of a patient. An abutment (made, for example, from titanium or zirconia) is then screwed (or placed or cemented) onto the top of the implant and is then adjusted by the dentist using dental tools. At this point, the abutment may be digitized by a 3D scanner, and a crown model generated using CAD techniques, and finally a physical crown (or appliance) milled out of a dental material such as ceramic, composite or metal. The abutment is scanned at the time it is customized (placed), i.e., at the time that the implant is first inserted. When customization of the implant is completed, either the abutment is removed for scanning outside the mouth, or the abutment is scanned inside the mouth while attached to the implant. U.S. Publication No. 20090087817, assigned to D4D Technologies, LLC, describes this approach.
Helical (or spiral) cone beam computed tomography (CBCT) is a known technique for three dimensional (3D) computer tomography in which a source (typically X-rays) describes a helical trajectory relative to an object being scanned while a two dimensional (2D) array of detectors measures the transmitted radiation on part of a cone of rays emanating from the source. Cone beam 3-D dental imaging systems provide dentists and specialists with high-resolution volumetric images of a patient's mouth, face and jaw areas. Three-dimensional views of all oral and maxillofacial structures allows for more thorough analysis of bone structures and tooth orientation to optimize implant treatment and placement, selection of the most suitable implant type and angulations prior to surgery. Representative commercial systems implementing these technologies are the i-CAT from Imaging Sciences International, Inc. and the GXCB-500 (powered by i-CAT) from Gendex Dental Systems, Inc.
Thus, it is well-known to use different imaging modalities (e.g., CT, MRI, OCT, ultrasound, microscopy, camera-based, etc.) to produce images for dental CAD CAM systems. In one use case, such as the planning for implant surgery, a first modality may be used to produce a scanned surface map of a patient's existing dentition, and a second modality may be used to produce 3D cone beam computed tomography data. Of course, each of the data sets provides different information, and it is desirable to provide a mechanism to align such data. While there are known techniques for this purpose, such techniques often produce less than optimal results. Errors in alignment may manifest themselves as distortions in an end result. For example, an alignment error between the 2D surface map and the 3D computed tomography data may result in inaccurate positioning of a dental implant device with respect to landmarks in either or both data sets. Moreover, because the data sets typically are acquired from significantly different imaging modalities, the characteristics of the data may be quite different, which exacerbates the problem for an automated solution. Due to these issues, most automated and semi-automated approaches to align such data sets may yield significant alignment errors. As a result, there is a need to provide a robust mechanism to allow users to visualize alignment errors, and to manually or automatically correct them.